A Theory for the RF Surface Field for Various Metals at the Destructive Breakdown Limit Metadata

Title

• Main Title A Theory for the RF Surface Field for Various Metals at the Destructive Breakdown Limit

Creator

• Author: Wilson, Perry B.
  Creator Type: Personal
  Creator Info: /SLAC

Contributor

• Sponsor: United States. Department of Energy.
  Contributor Type: Organization

Publisher

• Name: Stanford Linear Accelerator Center
  Place of Publication: [Menlo Park, California]
  Additional Info: SLAC

Date

• Creation: 2007-03-06

Language

• English

Description

• Content Description: By destructive breakdown we mean a breakdown event that results in surface melting over a macroscopic area in a high E-field region of an accelerator structure. A plasma forms over the molten area, bombarding the surface with an intense ion current ({approx} 10{sup 8} A/cm{sup 2}), equivalent to a pressure of about a thousand Atmospheres. This pressure in turn causes molten copper to migrate away from the iris tip, resulting in measurable changes in the iris shape. The breakdown process can be roughly divided into four stages: (1) the formation of ''plasma spots'' at field emission sites, each spot leaving a crater-like footprint; (2) crater clustering, and the formation of areas with hundreds of overlapping craters; (3) surface melting in the region of a crater cluster; (4) the process after surface melting that leads to destructive breakdown. The physics underlying each of these stages is developed, and a comparison is made between the theory and experimental evidence whenever possible. The key to preventing breakdown lies in stage (3). A single plasma spot emits a current of several amperes, a portion of which returns to impact the surrounding area with a power density on the order 10{sup 7} Watt/cm{sup 2}. This power density is not quite adequate to melt the surrounding surface on a time scale short compared to the rf pulse length. In a crater field, however, the impact areas from multiple plasma spots overlap to provide sufficient power density for surface melting over an area on the order of 0.1 mm{sup 2} or more. The key to preventing breakdown is to choose an iris tip material that requires the highest power density (proportional to the square of the rf surface field) for surface melting, taking into account the penetration depth of the impacting electrons. The rf surface field required for surface melting (relative to copper) has been calculated for a large number elementary metals, plus stainless-steel and carbon.
• Physical Description: 15 pages

Subject

• Keyword: Copper
• Keyword: Breakdown
• STI Subject Categories: 43 Particle Accelerators
• Keyword: Shape Accelerators,Accphy
• Keyword: Field Emission
• Keyword: Power Density
• Keyword: Penetration Depth
• Keyword: Physics
• Keyword: Melting
• Keyword: Electrons
• Keyword: Carbon
• Keyword: Accelerators
• Keyword: Accelerators,Accphy
• Keyword: Plasma

Source

• Journal Name: AIP Conf.Proc.877:27-40,2006; Conference: Invited tutorial presented at 12th Advanced Accelerator Concepts Workshop (AAC 2006), Lake Geneva, Wisconsin, 10-15 Jul 2006

Collection

• Name: Office of Scientific & Technical Information Technical Reports
  Code: OSTI

Institution

• Name: UNT Libraries Government Documents Department
  Code: UNTGD

Resource Type

• Article

Format

• Text

Identifier

• Report No.: SLAC-PUB-12354
• Grant Number: AC02-76SF00515
• Office of Scientific & Technical Information Report Number: 900599
• Archival Resource Key: ark:/67531/metadc884571

Note

• Display Note: http://www.slac.stanford.edu/cgi-wrap/pubpage?slac-pub-12354.html